Bacon Frittata Focaccia Sandwiches

Name: Bacon Frittata Focaccia Sandwiches
Ingredients: 4 3/4 cups (618 grams) bread flour; 1 tablespoon sugar; 2 1/4 teaspoons instant yeast; 2 teaspoons kosher salt; 2 cups (480 grams) warm water; 6 tablespoons olive oil, divided; Flaky salt; Nonstick cooking spray, for the sheet pan; 2 tablespoons olive oil; 1 small yellow onion, thinly sliced; 1 small zucchini, thinly sliced; Kosher salt and freshly ground black pepper; 3 ounces (85 grams) shredded white Cheddar; 8 large eggs; 3/4 cup (180 milliliters) whole milk; 1/2 cup (120 milliliters) heavy cream; 1 tablespoon gochugaru or a few sprinkles of crushed red pepper; 10 slices American cheese; 1 pound cooked bacon; Ketchup, for serving